The present invention relates to an X-ray radiographing system used for non-destructive tests and medical image diagnoses, and in particular, to a digital phase contrast X-ray radiographing system capable of obtaining X-ray images having high sharpness and high image quality.
X-ray penetrates material, and when X-ray penetrates material, the X-ray is absorbed by photoelectric effect and Compton scattering performed by an atom of which the material is composed. The absorption amount of X-ray depends upon an atomic weight. Accordingly, after X-ray penetrates the material, X-ray image is obtained by the acquisition of the X-ray intensity distribution that is two-dimensional, based on the distribution of the atom. The X-ray intensity difference generated as an image density obtained here is called absorption contrast generally. Since the discovery of X-ray by Dr. Roentgen in 1895, this is the principle used as X-ray image.
On the other hand, in the 1990s, the research about the phase contrast X-ray image started widely. X-ray has a nature that is the same as that of light, because X-ray is an electromagnetic wave. That is, refraction and interference are generated. The X-ray intensity difference obtained by this nature is called the phase contrast. It was found that the edge of the absorption contrast image in the past is depicted sharply by the phase contrast. However, as compared with visual rays, a refractive index of X-ray is extremely small, the phase contrast image was not observed in the conventional X-ray radiographing method. Further, since the wavelength of the X-ray is shorter than that of the visual rays by about three figures, it is extremely difficult to obtain the phase contrast image by controlling interference, and at present, a stage is for research, and not a stage of its wide use in hospital.
There is reported the methods in which a sharp X-ray image is obtained by acquiring an edge-enhanced image that is so-called the one having enhanced edge of the image, using the nature of refraction of X-ray. That is, there is the journal of Medical Physics, page 2190, issue 10, volume 26 by Mr. N. Yagi, for the case that radiation X-ray from synchrotron is used, for example, and further, there is the journal of the Optical Review, page 566, issue 6, volume 7 (1999) by Mr. A. Ishisaka, for the case Coolidge X-ray tube (electro-thermal X-ray tube) is used. Concerning the methods for obtaining a phase contrast X-ray image that is edge-enhanced by using interference of X-ray, there is the journal of Nature, page 335, volume 384 (1996), by S. W. Wilkins, or an official report of Patent WO96/31098, for the case that a special Coolidge X-ray tube having microscopic size of focal spot is used, or there is disclosed on the official report of TOKKAIHEI 9-187455, for the case that the principle of an interferometer is applied by using the above-mentioned radiation X-ray.
This invention is the one relating to the X-ray radiographing system that can obtain X-ray image having high sharpness, using the refraction of X-ray. To radiograph the sharp X-ray image by refraction, there are used a non-screen X-ray film, one in which X-ray intensifying screen and X-ray film are used, or a very small CCD camera whose pixel size is about 10 μm. The foregoing is because it has been thought that very high resolving power is necessary for radiographing the enhanced edge formed by the refraction of X-ray.
Here, in the case of a non-screen X-ray film, or in the case of one in which X-ray intensifying screen and X-ray film are used, the resolving power is very high, however, they are so-called analog X-ray image detector, and it is impossible to perform freely image processing or magnification/reduction of output image.
Further, in order to obtain a digital X-ray image, it is possible to use X-ray detector by using CCD having high resolving power, but CCD section is required to be cooled to keep sufficient sensitivity, and the apparatus turns out to be very expensive, and due to this, it is used only for the particular research in a limited area.